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TACO zone valves cycle slowly??

notnim Member Posts: 2
I replaced my 3 old B&G modumate zone valves with TACO 24V, two way model 571-2 valves last year, they operate just fine except that when opening and closing the contacts make and break in rapid succession, causing my burners to ignite and reignite several times before either starting up or shutting down, I realize the heat motors take time to cycle but sure would like to eliminate this as it seems like a lot of wear and tear on the gas valve and I worry that sometime it could cause excessive gas buildup when igniting. I should mention I have a LP gas fired Burnham boiler with a standing pilot. Looking for a solution??


  • STEVEusaPA
    STEVEusaPA Member Posts: 5,695
    Check all your low voltage wiring, and the thermostat. Then check t-t or x-x at the aquastat.
  • Dave H_2
    Dave H_2 Member Posts: 503
    It depends upon how they are wired. If wired to a ZVC controller, then there should be no problem like you are experiencing. Then check the wires as @STEVEusaPA mentions.

    If you are using the end switch from the zone valves straight to the boiler, then I would suggest using a ZVC. The 571 zone valves will intermittently open and close power when opening. This design is on purpose because these are a very large power draw valves (21VA) and the intermittent opening is to allow upto three on a 40VA transformer. Using a ZVC controller will eliminate the intermittent call to the boiler.
    Dave H
    Rich_49CanuckerSteve Thompson (Taco)
  • notnim
    notnim Member Posts: 2
    Yes ,the zone valves go straight back to the boiler, I will be checking into the ZVC controller, thanks very much!
  • unclejohn
    unclejohn Member Posts: 1,757
    I would suggest you use a separate 75va transformer and a isolation relay.
  • ChasMan
    ChasMan Member Posts: 459
    How does the ZVC solve this issue exactly? Are you saying there are some smarts in it to overcome a chattering end switch? I have a pair of them on my workbench. Whenever I open the end swtch contacts on any zone the xx contacts open. I didn't notice any delay in it happening either.
  • hot_rod
    hot_rod Member Posts: 16,344
    The way that ZV operates is it goes open and overstrokes, drops back and repeats the cycle. If you connect it to an O-scope and data logger you can observe that operation, it is around a 17 second pulse. as Dave mentioned it is an attempt to lower power consumption as opposed to keeping it at a constant 21VA draw.

    I never have never known them to drop off the end switch when it cycles to save power? Sounds like a bad valve? If in fact that is what is going on. Observe it with a heat call for about 30 minutes to see the cycling.

    Could the thermostat be causing the drop off? Wire the ZV to a constant 24V and see of it behaves, that eliminates the stat question.

    I agree a relay box will not cure the issue if it is in the valve itself.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • ChasMan
    ChasMan Member Posts: 459
    I guess you could jump the end switch in the ZVC then the thermostat would run the boiler but that seems like a hack. Probably just bad wiring.